In general, fog begins to form when water vapor in atmospheric air condenses into tiny water droplets at or near a cool water surface or ground surface. In order to form many tiny water droplets from water vapor in atmospheric air such as fog, the following conditions have to be met.                There must be sufficient water vapor in the atmospheric air        Air must cool to a temperature equal to or lower than a dew point        Many condensation nuclei, which are tiny hydroscopic particles for accelerating condensation of water vapor into tiny water droplets in the atmospheric air, must be suspended in the atmospheric air        A water vapor supply source must exist nearby.        
When air cools under these conditions, fog occurs. In areas in which fog occurs, it is very important to secure good visibility of drivers, captains, or pilots when cars run on roads, ships enter or leave harbors, or airplanes enter or leave airport runways. Fog, a natural phenomenon resulting from a rapidly changing temperature, greatly reduces visibility, thereby substantially hindering safe operations.
That is, a pilot who operates an airplane may not secure a sufficient visual range in thick fog so that the airplane may not safely take off or land. In particular, when the airplane is to land and thick fog occurs over an airplane runway, since the pilot has to take the airplane to another airport, passengers may feel discomfort and an airline may suffer huge losses.
Also, there are areas in which fog regularly occurs along highways on which cars travel. Fog is one of the most dangerous factors in blocking visibility of drivers on roads. The frequency of accidents due to fog that hinders safe operations is actually high, and the risk of chain collisions may increase due to fog.
Accordingly, to solve these problems, methods of further improving forward visibility by mounting a fog lamp on the front of a car or blinking an emergency lamp have been used. However, since these methods greatly reduce driving speeds of cars and thereby obstruct smooth traffic flow and cause traffic jams, economic losses are incurred. Also, since these methods do not fundamentally remove fog, similar accidents repeatedly occur in areas in which fog regularly occurs, thereby leading to mass casualties.
Fog is classified into various types based on various factors such as causes or geographical features. There is fog that occurs in a certain region and is stagnant from the ground to a high altitude, and fog that occurs in a region and moves along the ground. In the case of the latter fog which moves along the ground, the fog may be prevented to some extent from entering onto a road and reducing visibility of drivers by installing physical barrier walls along both boundary sides of a road. In fact, however, the barrier walls may physically block fog but do not remove fog. As a result, since fog traveling along the ground rises and falls along the barrier walls and enters onto the road, it is difficult to expect that the barrier walls may block fog and thus prevent various accidents due to fog on the road, and costs of installing the barrier walls are high.